What convinced that it would not work was reading about the temperature pressure differences the on car motor was supposed to handle. It sounds like there needs to be a giant air compressor strapped to the car. Having been in a garage when an air compressor turns on (unpleasant), I really don't want to be in a tiny metal tube with a giant air compressor on all the time. It sounds several times worse then being in an airplane.
The compressor in your garage is almost certainly a reciprocating compressor (oscillating motion = very loud), while the hyperloop uses an axial compressor (pure rotary motion = much quieter).
The same sound absorbing layers and vibration isolation technology that's used on jet planes could also be used if needed.
There would be no sonic "shock wave" killing everyone in the tube in the event of a breach. Viscous drag on the tube walls would reduce the flow velocity to highway speed in only a couple km. The wave front spreads out, becoming a gradual pressure rise.
The entire tube would be designed for rapid repressurization (under 60 seconds). The cars can easily stop in 15-20 seconds since the passengers are strapped in and possibly in seats facing backward to arrest braking forces.
Expansion joints are easily accommodated at the end stations, and the slight leaks from the sliding interfaces are compensated by mechanical pumps (easy to maintain 1/1000th of an atmosphere, damn near impossible to maintain 1/1000000 of an atmosphere for true vac trains given the linear decrease in vacuum pumping mass flow at low pressures and the need for turbomolucular pumps and/or cryopumps at those pressures).
There's a great need for pumping near the end stations anyway due to residual air entering around the pod in the airlock. They'll pump down the majority of the pressure of course, but due to the exponential drop in pumping speed over time it makes little sense to make passengers wait a long time and pump it down to the exact same pressure when they can cut it off early and just let the tube pumps make it up. Even on the space station (where air is very expensive) they only pump the airlock down part-way and vent the remaining residual atmosphere so the astronauts (whose time is also expensive) don't have to wait.